webadmin: fix findbugs warning on ProviderModel

This patch fixes a findbugs warning in ProviderModel, as we case a
variable that's known to be null.
The fix just passes null, and in order to be able to address the
ambiguity, the method name was renamed according to the use-case.

Change-Id: I94c5ff1cde5c76a89ea0c56022e306a264905066
Signed-off-by: Oved Ourfali <oourfali@redhat.com>